The presence of both .mkv and .mp4 is redundant. In most operating systems, the "real" extension is the last one ( .mp4 ). The .mkv is likely part of the filename itself to trick users who expect a specific video container.
Right-click the file and check the "Type of file" in your system settings to confirm it is actually a video and not an application ( .exe , .scr , or .bat ). honeym00n.mkv.mp4
A real video file should be several megabytes or gigabytes. If the file is only a few kilobytes, it is likely a script or a shortcut. The presence of both